US2378894A - Generator - Google Patents

Description

y PatentedY June 26, 1945 2,378,894 GENERATOR J ohn E. Blankenbuehler, Edgewood. Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application `July 24, 1943, Serial No. l195,980

(Cl. P11-228) 6 Claims.

My invention relates generally to generators, and it has reference in particular to arc welding generators of the cross-eld type.

Generally stated, it is an object of my invention to provide in a simple and inexpensive manner for improving the arc welding characteristics of cross-iield generators.

More specifically, it is an object of my invention to provide for increasing the open circuit arc striking voltage of arc welding generators of the cross-field type without causing-undesirable commutating conditions at the auxiliary brushes.

It is also an object of my invention t provide for improving the commutating characteristics at the auxiliary brushes in a generator of the crossiieici type.

Another object of my invention is to provide a simple method of increasing the open circuit voltage of existing generators of the cross-field type by providing suillcient auxiliary excitation ci the field windings to increase the no-load circulating current in the auxiliary brush circuit, and utilizing a commutating pole positioned at the point oi maximum amature potential relative to the main brushes for preventing undesirable commutation at the auxiliary brushes.

Yet another object of my invention is tc provide increased auxiliary excitation of a iield pole winding in a generator of the cross-ileld type and connect a commutating pole winding in the auxu iliary brush circuit to neutralize .the eiect o: the increased excitation on the commutation at the auxiliary brushes.

Other objects will in part be obvious, and will in part be explained hereinafter. i

In practicing my invention in onev form thereof, the auxiliary excitation usually applied to the series iield windings of generators of the crossiield type for determining the polarity of the main load brushes is increased suifioiently to in crease the open circuit voltage available at the main brushes, tor the purpose of improving the are etiilauiv: characteristics' of the generator. A oommutatiugpole is positioned to one side or the armature ,substantially intermediate the vmain nel@ polo meinimrc and is provided with a commutatine winding connected in series circuit re lation with the auxiliary brushes for neutralizing the otherwise harmful eiects or the increased auxiliary excitation ouJ commutation at the auxiliary brushes. l

For a more complete understanding of the nature and scope .ci my mventiomreferenee may be had to the following detailed description which `weil known may be read in connection with the drawing, in which:

Figure 1 is a diagrammatic view of an arc welding system embodying the principal features of the invention; and

Fig. 2 represents load characteristic curves of a cross-Held generator before and after embodying features of the invention.

Referring to Figure 1, the reference numeral' lli may denote generally an arc welding generator of the cross-eld type which is arranged for supplying welding current to an electrode ll for performing a welding operation on work I2.

The generator Ill may comprise, generally a frame I3 of magnetic material having eld pole members l5 and i6 positioned therein in opposed relation. The field p'ole members comprise body portions I8 and I9, respectively, which are positioned adjacent the frame i3 and surrounded by series field windings 20 and 2|. The body members IB and I9 are preferablyV of a relatively small cross-section, so that they saturate at the values of welding current well below the normal range of welding current.

The eld p ole members may also be provided with enlarged arcuate shoe portions 23 and 24, respectively, having recessed central portions 26 and 21 with central projections 28 and 29, respectively, for accommodating compensating windings 3l and 32 in a manner well known in the art. Means. such as the supports 34, may be provided between the arcuate shoe portions and the frame adjacent the ends of the shoe portions to provide a more rigid mechanical structure. These supports are preferably of a non-magnetic materia-i, such as brass.

The generator may be provided in the usual manner with an armature 3B positioned intermediate the arcuate shoe portions oi the field pole members. Auxiliary brushes 3o may be provided for they armature, being positioned along en axis substantially perpendicular to 'the axis of the eld pole members Main brushes 3S may be positioned substantially along the oi the @leid pcie members and connected in series circuit relation with the series held windings Eil and the compensating windings 3i and ci., elec trede i i and work t2,

Suitable means may be provided in a manner in the art for controlling the output ci the generator such. as, ior example., the magnetic shunt member 40 which may be supported adjacent'the tips of the arcuate shoe members 23 and It and to one side of the armature 36 by support plates Il which4 may be secured to the polarity of the generator ill,I suitable auxiliary excitation may be providedv for either one or both of the iield polewindings 2l and 2|, or an additional eld winding connected to a source of auxiliary excitation may be provided in a manner well known in the art for maintaining the residual polarity of the field pole members in a predetermined direction. For example, a source of unidirectional current may be provided by connecting a rectifier bridge circuit 42 to a suitable source of alternating current 43 and utilizing a reversing switch 44, together with conductors and 4E, to connect the unidirectional source across the series field windings Zland 2i and the compensating windings 3| and 32.

In order to provide for increasing the normal open circuit voltage available at the electrode ii for striking an arc on the work i2, the amount of auxiliary excitation produced by the auxiliary source 4| may be increased to a value in excess of the usual polarity control excitation. In one instance, for example, with a cross-field generator of the type illustrated, I have found that, by increasing the voltage available at the auxiliary source 4I sui'ilciently` to increase the auxiliary excitation of the series i'ield windings 2li and 2i at no-load from approximately l to 16 amperes, it is possible to increase the open circuit voltage of the generator from 45 to 60 volts. This greatly improves the arc strikingcharacteristics of the generator and improves the quality of the welds produced. With an increase of the auxiliary excitation, the residual or no-load magnetic flux in the body portions of the field pole members I5 and i6 is increased correspondingly. Accordingly, the circulating current which flows in the auxiliary brush circuit due to the armature conductors cutting the residual magnetic flux when the generator is running at no-load, will be increased substantially in proportion. This increase of current in the auxiliary brush circuit creates an undesirable commutation condition at the auxiliary brushes resulting in arcing of the brushes.

In order to improvecommutation atv the 'auxiliary brushes, and to neutralize or compensate for the increased current in the auxiliary brush circuit, a commutating pole Il may be positioned to one side of the armature 36, substantially in-v termediate the field pole members i5 and I B. A winding 49 may be positioned on the commutating pole 48 and connected in series circuit relation with the normally short-circuited auxiliary brushes 38. By providing the winding 48 with a number'of turns approximately equal to 'two and one-half times the number "of armature turns which are effective to produce a magnetic flux opposing that of the commutating pole 4I, I have found that highly satisfactory operation of the generator may be secured even with the increased current in the auxiliary brush circuit.

It will be noted that the ratio of commutating field pole turns to opposing armature turns is 4substantially greater in the case of a cross-iieldl generator than with generators of the usual type where it is common to operate with only one and one-quarter times the number of turns opposing amature turns on the commutating pole.

Since the cross-field type of generator is inclined to be relatively critical as to commutation even where the no-load voltage is not increased, and where polarity control excitation is not used, a commutating pole may be used to advantage in accordance with my invention. A symmetry of the air gap or misalignment of the field pole members, which usually result in substantial increases of no-load auxiliary brush current. can readily be neutralized by the use of a commutating pole which may be positioned intermediate the main iield pole members on one side of the armature where a single magnetic shunt is used on the other side oi' the armature. lower grades of brushes may be used with a oommutating pole, whether or not the current is increased, thereby aifording an appreciable saving.

Referring to Fig.' 2, the letter a designates a typical load characteristic or volt-ampere curve of a 30D-ampere arc welding generator of the cross-field type embodying the features of the invention. The dotted curve b represents a typi- A cal load characteristic or volt-ampere curve of the same generator before embodying the features of my invention. It will be, noted that the open circuit voltage of the generator has been increased from 45 to 60 volts, thereby greatly in'iproving the arc striking characteristics lof the generator.

Since the curves a and b merge at the point c where saturation of the body portions of the field.

pole members effectively determines the load characteristic curve, the load characteristics oi' a cross-iield generator embodying the features oi the invention are not affected within the normal operating range of the generator.

The curves d and e represent variations in-the auxiliary lbrush circuit current corresponding to the different values of load current. Thoughlthe auxiliary brush current at no-load is increased tained without material alteration of the generator and at a minimum of expense and labor. Such an improvement is relatively important when it is considered that, in order to obtain the same results by redesign of the machine itself, the number of armature tunis, the size of the armature, the amount of iron therein, and also the-overall size of the machine would have to be greatly increased to obtain the same results. Under the present conditions, when copper and iron are vital materials, it will be realized that the invention is a valuable aid to the conservation of these materials, as well as an important improvement tofthe welding generator, and a valuable contribution to the arc welding industry.

Since different embodiments of the invention may be made and certain changes may be made in the drawing and description without departing from the spirit and scope of the invention, it is intended that all the matter contained in tho In addition,'

abovedescription or shown in the accompanying drawing shall be construed as illustrative and not in a limiting sense.

I claim as my invention: g

1. A generator comprising, a frame structure, an armature rotatably mounted in the frame structure and provided with main and auxiliary close-circuited brushes, a pair of field pole members supported by the frame structure havingv excitation windings thereon, circuit means providing sufficient auxiliary excitation to one of the said excitation windings to substantially increase the open circuit voltage of the main brushes, and an interpole structure positioned intermediate the tleld pole members on one side of the armature having a winding thereon connected between the auxiliary circuit brushes.

2. A cross-iield generator comprising, a pair of opposed iield pole members having excitation windings thereon, an. armature rotatably positioned between the eld pole members having main and auxiliary brushes, circuit means connecting at least one Aof the field pole excitation windings to a separate source of excitation, and

yan interpole structure positioned intermediate the iield pole members having a commutating winding thereon connected in series relation with the auxiliary brushes to compensate for the auxiliary brush commutation conditions caused by i series circuit relation to the auxiliary brushes.

4. A generator comprising, an amature having a commutator with pairs of main and auxiliary ing a pair of iield pole members on opposite sides o! the amature having windings connected in series circuit relation with the main brushes. and a commutating field pole member positioned substantially along the axis of the auxiliary brushes having a winding connected in series circuit relation with the auxiliary brushes.

5. An arc welding generator having an armature with main and auxiliary brushes, a pair o! field pole members having excitation 4windings connected in series with the main brushes, circuit means connecting the field pole windings to a source of auxiliary excitation of sufilcient voltage to raise the open circuit voltage of the main brushes, and a commutating pole positioned on one side of the armature substantially iliary brushes positioned along axes electrical degrees apart, a frame having opposed main neld pole members with ileld windings thereon con nected in series circuit relation with the main brushes, means including a reversing switch for applying sumcient auxiliary excitation to one of lthe eld windings to increase the residual ilux in the main field polel members whereby'the noload circulating current in the auxiliary brush circuit is increased suiilciently to produce the desired open circuit voltage, and means including a commutating iield pole member intermediate the main iield pole members having a commutating winding thereon connected in series circuit relation with the auxiliary armature brushes to correct undesirable commutation conditions produced by the effects of-the auxiliary excitation at no load. y

JOHN H. BLANKEN'BUEHLER.

Images